Chosen Solution

This is actually an answer rather than a question; a solution to a problem that is not yet in any guides. Since I couldn’t find a resolution online, I figured I’d share my own. The mid 2017 21.5" model of the iMac is new and this issue isn’t major, so it’s not surprising that the few people who have sewn up their computers after an upgrade or fix either haven’t encountered it yet, or found the true cause. The problem is that after reassembly, the microphone input is faint and muffled. It functions, but barely, and is essentially unusable. The culprit turns out to be the adhesive strips used for reassembly. The frame of this iMac model seems identical to its 2012-2015 predecessors, so ostensibly the same strips made for these earlier models would work here too. However, the microphone has been moved from the top of the computer (near the webcam) to behind the frame at the bottom of the screen. Note the location of the “4R” strip in the following picture: https://d3nevzfk7ii3be.cloudfront.net/ig… Now look at the location of where the microphone has been moved to: https://d3nevzfk7ii3be.cloudfront.net/ig… One can clearly see that the “4R” strip completely covers the microphone and the holes in front of it, deadening any sound picked up. Knowing this, the solution is simple. Make sure the microphone works properly before using any adhesive. Then, apply the adhesive strips, but when laying down the “4R” strip, cut away the portion covering the microphone (and a little bit more from each side to be safe). Hopefully, this post will save others from hours of exasperation! :) Cheers!

@iofile Better go here and create a technique tutorial about this it will be more efficient than a answer in a question. If you dont want to do it just tell me and I will enjoy doing it in your place.

for future fixers, here’s some verification of the above info. The first photo is how I found the adhesive as soon as I peeled it off, clearly a clean cutout of the adhesive from the factory for the microphone. And then the second photo after I uncovered the other two holes.

Hi! For anyone who ends up here in / after 2019, our iMac Intel 21.5" Retina 4K Display (2017) Adhesive Strips Replacement guide accounts for this issue, and all corresponding procedures link to that guide. Happy fixing!

Eve Ann Wallis - This series has a unique issue! Apple moved the microphone hole! And in doing so have messed up a few people. You need to modify the bottom tape with a small cut out so the hole is not covered. Here’s the location of the microphone hole:

At this point you should get another adhesive tape kit and after fully cleaning the old tapes off, modify the new set as needed but cutting a small area at the bottom edge of the strip where the mic is and give that a go! But, before you put the display back on check your mic cable is connected properly as outlined in step 57 in this guide and the ribbon cable is not damaged iMac Intel 21.5" Retina 4K Display (2017) Logic Board Replacement